1. Field of the Invention
This invention relates to a novel sugar chain and, more particularly, to a novel sugar chain which is useful for the diagnosis and treatment of cancerous diseases.
2. Description of the Background Art
Sugar chains existing on cell membranes combine with proteins, lipids, and the like. They are present as glycoproteins, glycolipids, or the like widely in living bodies. Glycoproteins to which sugar chains bond play important rolls in the control of physiological functions as enzymes or hormones, or as factors for controlling osmotic pressure and the like. There are glycoproteins which function to transfer physiologically active substances such as medicines to the target organs. Thus, glycoproteins are very important substances for the living bodies. Almost all plasma proteins are said to be glycoproteins.
Blood-type antigens are known as important sugar chain antigens which are present on the surface of cells. Besides ABO (H)-type blood-type antigens which are well known in the art, there are sugar chain-containing blood-type antigens such as Lewis-type, Ii-type, and R-type [J. M. McKibbin, et a., J. Biol. Chem., 257 (2), 755-760 (1982); K. 0. Lloyd, et al., Immunogenetics, 17, 537-541 (1983)].
Glycolipids changes in various way along with canceration of cells. Such glycolipids are therefore considered to be cancer-related cell membrane antigens. Extensive studies are ongoing for their applications to the diagnosis and treatment of cancer [A. Brown, et al., Bioscience Reports, 3, 163-170 (1983); S. Hakomori, Biochem. Biophys. Res. Commun., 113 (3), 791-798 (1983)].
Quite a few autoantibodies which are found in autoimmune diseases recognize sugar chain antigens of itself. In this instance, the sugar chain antigens play an important role as autoantigens.
The receptors for peanut agglutinins (PNA) are confirmed to be produced in a number of human carcinomas. The present inventors have tried to clarify the sugar chain structure of the receptors as part of the studies related to the investigation in the mechanism by which the receptors are produced. As a result, the inventors could determine the structures of di- and tetra-saccharide which are the major components of O-linked sugar chains produced by an alkaline NaBH.sub.4 treatment of the receptors [N. Shimoda, et al., J. Biochem., 102, 657-664 (1987)].
As mentioned above, sugar chains combined with proteins and lipids have important functions in the maintenance of life in living bodies. Identification of sugar chains therefore is expected to lead to the clarification of their more definitive functions and involvements in various diseases and is considered to be useful for the diagnosis and treatment of diseases.